Dec 15 2014
White-throated sparrows come in two color morphs: white-striped shown above, tan-striped below. The crisp white-striped birds aren’t always male, the plain tan-striped birds aren’t always female. You can’t tell their sex by color.
Here they are side-by-side: white-striped on left, tan-striped on right. Notice that …
- Head stripes are black-and-white versus brown-and-tan
- Lores are bright yellow versus dull yellow
- Malar stripe is weak versus prominent
- Breast is gray versus brown-and-tan
- Breast is mostly clear versus very streaky
Not only do they look different but the white-striped birds are aggressive, philandering and don’t take much care of their kids while the tan-striped birds are gentle and very caring of their young.
You would think these differences would force one of the color morphs to disappear from the gene pool but it doesn’t. The reason is surprising.
When it comes to picking mates, these birds always mix it up. White-striped (aggressive) males mate with tan-striped (care-giving) females and the tan-striped (gentle) males mate with white-striped (philandering) females. Thus the color morphs and personalities persist.
And when you see white-throated sparrows you’ll know you can’t tell their sex by their color but the drab ones are always good parents.
(photos: White morph white-throated sparrow from Wikimedia Commons, Creative Commons license. Tan morph by Henry McLin on Flickr, Creative Commons license. Click on each photo to see its original)